The present invention relates to a beverage package and a method of packaging a beverage. It particularly concerns beverages having in solution gas, typically nitrogen and/or carbon dioxide, which is to be liberated to develop a head of foam or froth on the beverage for consumption.
The invention was primarily developed for the packaging of fermented beverages such as stout, lager, ale (or other beer) or cider although it is to be realised that it can be applied to the packaging of other alcoholic beverages, such as spirits and wines, or to non-alcoholic beverages such as so-called soft drinks, milk shakes and the like. In the packaging of beverages in a sealed container such as a can or bottle it is recognised that the presence of air or oxygen, particularly in a headspace of the container, can cause oxidation of the beverage and consequential adverse changes in its desirable characteristics (such as in the taste, bouquet or mouth feel). The presence of oxygen in close proximity with a beverage, even in relatively minute proportions of volume of oxygen to volume of beverage, can drastically shorten the shelf life of a sealed beverage package. Consequently, considerable care and measures are taken in beverage filling lines, particularly for beer, in an attempt to remove air from the container prior to sealing or to ensure that the air/beverage ratio is at an acceptably low level consistent with achieving a desired shelf life for the package. A sealed package for beer desirably has a shelf life in the order of 10 to 12 months so that at any time during that period a consumer opening the package can expect a product which is substantially consistent in its desirable characteristics.
Many beverage packaging techniques have been developed and incorporated in container filling lines to alleviate oxygen contamination by the presence of air in the container when sealed. Conventional techniques include purging the empty container of air with nitrogen or other non-oxidising gas, charging the container with beverage and thereafter taking steps to alleviate the entry of air into the headspace which is formed prior to the container being sealed. These latter steps can include, for example, filling the container headspace with froth or foam to displace air therefrom, dosing the headspace with liquid nitrogen so that nitrogen gas evolves and displaces air from the headspace or directing nitrogen gas under pressure into the headspace as the container is capped or sealed.
A beverage package which has achieved considerable commercial success is that in which, upon opening the sealed container, gas in solution from the beverage is intentionally liberated within the container to develop froth or foam in the container headspace. This purposeful liberation of the gas, particularly nitrogen, in solution may be achieved by many techniques which we have developed and are now well known in the art. For example, the beverage can be subjected to ultrasonic stimulation or to an externally developed jet of gas or liquid (conveniently applied from a syringe) in accordance with the disclosure in our British Patent No. 1,588,624 or an internally developed liquid (beverage) and/or gas stream may be injected into the beverage in accordance with the disclosure in our British Patent No. 2,183,592A.
In beverage packages in which the gas in solution is intentionally liberated to form froth or foam in the headspace when the sealed container is opened, it is usual to ensure that the headspace is of an adequate size to accommodate the froth or foam which will develop (or which will develop in a reasonable time prior to the beverage being poured from the container, say into a drinking vessel) so that the likelihood of the froth or foam bubbling out of the container and the beverage thereby being wasted is alleviated. It is common practice therefore that the volume of the headspace of a container in which the gas in solution is, or is to be, intentionally liberated on opening the container is considerably greater than the headspace of a beverage container in which it is not intended that the gas in solution should be liberated purposely within the container. In a typical example, a beverage can containing 500 milliliters of beer having gas in solution which is not intended to be intentionally liberated on opening of the container may have a small headspace or vacuity in the order of 27 milliliters (in practice this means that with a conventionally proportioned beer can the headspace has a depth of approximately 8 millimeters). In comparison a similarly dimensioned beverage can may contain 450 milliliters of beer having gas in solution which is to be liberated intentionally within the can on opening so that its headspace is relatively large, say with an approximate volume of 70 milliliters and a depth of approximately 20 millimeters.
With conventional containers having small sized headspaces as aforementioned, the removal and/or exclusion of air/oxygen from the headspace prior to sealing can be achieved in a relatively simple and efficient manner on a high speed container filling and sealing line simply by blowing nitrogen gas across or through the headspace prior to and as the container is sealed. However, with packages having the relatively large volume and deep headspace as aforementioned, simple blowing with nitrogen gas has been found unacceptable to ensure adequate removal of air/oxygen from the sealed container. Consequently to achieve this latter aim it is usual to employ additional de-gassing techniques and a currently popular air/oxygen purging step is to introduce a dose of liquid nitrogen into each container in the packaging line. The nitrogen gas which evolves from the dose displaces air from, and alleviates the entry of air into, the headspace so that such air/oxygen as may remain in the headspace is within acceptable tolerances as the container is sealed. The liquid nitrogen dose may also serve to pressurise the contents of the container when the latter is sealed. However, liquid nitrogen dosing is an expensive facility in a packaging line both in installation costs and running/consumable costs. Also it is disadvantageous in so far as it restricts the speed at which a packaging line can run and it is difficult to ensure, on a continuously moving line of containers, that the dose of liquid nitrogen which is introduced into the headspace of each container is consistent within predetermined tolerances (so that if the liquid nitrogen dose serves to pressurise the container when sealed, it is difficult to maintain consistency in the internal pressures of the sealed containers which issue from the packaging line). It is an object of the present invention to provide a beverage package and a method of packaging a beverage in which the beverage in the package contains gas in solution that is intentionally or purposely to be liberated to form froth or foam in a relatively large headspace of the container and which lends itself to alleviating the difficulties associated with conventional packaging techniques as discussed above.